Can the executables with the same names as shell builtins get away with doing a lot less "work" than the shell builtins do? For instance, could the fg executable just exit abnormally immediately? Could the wait and jobs executable exit 0 if given no arguments and exit 1 otherwise?

So, on OS X, for instance, /usr/bin/cd and /usr/bin/wait are the following script(s):

It would be uncommon to actually use these external utilities as the builtins would be used first. It also looks like it could have unwanted consequences. For example, a script may use the external cd as a way of testing whether changing working directory would work, and then rely on the fact that an external cd would actually not change directory...
– Kusalananda♦Apr 1 at 8:00